It has long been that polyethylene terephthalate (PET) has superior physical properties, e.g., resistance to chemical attack, and desirable mechanical and electrical properties. Despite these superior physical properties, PET is not always the material of choice for injection molding usage because relatively high mold temperatures, e.g., 120.degree.-140.degree. C., must be utilized to insure good moldability. Any attempt to use a lower mold temperature, e.g., 100.degree. C. or lower, results in the injected material being unmoldable as, for one thing, the molded article sticks in the mold and often can only be removed with great difficulty. To circumvent this processing disadvantage, the molder is forced to select more expensive materials such as polybutylene terephthalate (PBT), inasmuch as this poly(alkylene terephthalate) is easily moldable even when using mold temperatures as low as 60.degree. C. By being able to use a lower mold temperature for PBT, the time necessary for cooling the injection molded article to a temperature at which it can be removed from the mold is considerably shorter than the cooling time necessary before the PET article can be removed from an initially hotter mold. Since this shorter cool-down period of PBT results in a shorter process cycle time and a higher rate of article production, economic justification exists for its use despite its higher unit cost.
Numerous nucleating agents for use in PET compositions are recognized in the art. For example, the following nucleating agents are known: salts of montan wax or of esters of montan wax in which the cation is metals of main groups I-III of the Periodic System (see U.S. Pat. No. 3,619,166); alkaline earth metal carbonates, e.g., calcium magnesium carbonate [CaMg(CO.sub.3).sub.2 ] (see U.S. Pat. No. 3,619,266 and British Pat. No. 1,239,455); oxides, e.g. titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, antimony trioxide and titanium dioxide (see U.S. Pat. No. 3,616,266, British Pat. Nos. 1,104,089, 1,111,012, 1,196,290, 1,239,455, 1,246,770 and translation of German No. 2,014,770); silicates, e.g. talc, sodium-aluminum silicate, CaSiO.sub.3, MgSiO.sub.3 (see U.S. Pat. No. 3,616,266 and British Pat. No. 1,111,012); lithium or sodium salts of polycarboxylic acids, e.g., succinic acid, adipic acid, suberic acid, 1,10-decanedicarboxylic acid, 1,4-cyclohexane-dicarboxylic acid, terephthalic acid, 1,2,3-propanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid, trimellitic acid, 1,2,3,4-cyclopentanetetracarboxylic acid and pyromellitic acid (see U.S. Pat. No. 3,761,450 and translation of German No. 2,014,770); carbon, e.g., graphite and carbon black (see British Pat. Nos. 1,104,089, 1,111,012 and 1,196,290); salts of alkaline earth metals, e.g., calcium carbonate and calcium sulphate (see British Pat. Nos. 1,104,089, 1,196,290 and 1,246,770); metals in a finely divided state, e.g., copper and antimony (see British Pat. Nos. 1,104,089 and 1,196,290); sulphates, e.g., CaSO.sub.4, BaSO.sub.4 and calcined gypsum (see British Pat. Nos. 1,111,012, 1,196,290 and translation of German No. 2,014,770); glass powder (see British Pat. Nos. 1,104,089 and 1,196,290); phosphates, e.g., Ca.sub.3 (PO.sub.4).sub.2 (see British Pat. No. 1,111,012 and translation of German No. 2,014,770); oxalates, e.g., calcium oxalate (see British Pat. No. 1,111,012); stearates, e.g., magnesium stearate (see British Pat. Nos. 1,111,012 and 1,181,679); benzoates, e.g., calcium benzoate and potassium benzoate (British Pat. No. 1,111,012 and translation of German No. 2,014,770); salicylates, e.g., zinc salicylate (see British Pat. No. 1,111,012 and translation of German No. 2,014,770); tartrates, e.g., calcium tartrate (British Pat. No. 1,111,012 and translation of German No. 2,014,770); neutral clays, e.g., "HITDRON" (British Pat. No. 1,111,012 and translation of German No. 2,014,770); sodium, lithium or barium salts of monocarboxylic acids, e.g., formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, caprylic acid, stearic acid, cyclohexane carboxylic acid, benzoic acid, p-tert-butyl benzoic acid, and naphthalene-1-carboxylic acid (see British Pat. No. 1,282,679); the disclosure of the foregoing references are incorporated herein by reference.
A welcome contribution to the art would be a PET composition which can be injection molded at relatively low mold temperatures (e.g., 100.degree. C. and below) to yield articles exhibiting good moldability characteristics, e.g., good mold releasability and desirable physical properties.